﻿using System;
using System.Collections.Generic;
using System.Threading;

namespace CSharpHelpers.Commons
{
    public delegate void UserWorkEventHandler<T>(object sender, WorkQueue<T>.EnqueueEventArgs e);

    /// <summary>
    /// 工作队列
    /// </summary>
    /// <typeparam name="T">泛型</typeparam>
    public class WorkQueue<T>
    {
        /// <summary>
        /// 表明处理线程是否正在工作
        /// </summary>
        private bool isWorking;

        /// <summary>
        /// 对isWorking的同步对象    
        /// </summary>
        private object lockIsWorking = new object();

        /// <summary>
        /// 实际的队列
        /// </summary>
        private Queue<T> queue;

        /// <summary>
        /// 队列同步对象
        /// </summary>
        private object lockObj = new object();

        /// <summary>        
        /// 绑定用户需要对队列中的item对象, 施加操作的事件        
        /// </summary>       
        public event UserWorkEventHandler<T> UserWork;

        public WorkQueue()
        {
            queue = new Queue<T>();
        }

        public WorkQueue(int n)
        {
            queue = new Queue<T>(n);
        }

        /// <summary>        
        /// 谨慎使用此函数，        
        /// 只保证此瞬间，队列值为空        
        /// </summary>        
        /// <returns></returns>        
        public bool IsEmpty()
        {
            lock (lockObj)
            {
                return queue.Count == 0;
            }
        }

        /// <summary>
        /// 单线程执行
        /// </summary>
        private bool isOneThread = true;

        /// <summary>       
        /// 队列处理是否需要单线程顺序执行        
        /// ture表示单线程处理队列的T对象        
        /// 默认为true，表明按照顺序出队， 单线程处理item       
        ///  *****注意不要频繁改变此项****        
        /// </summary>        
        public bool WorkSequential
        {
            get
            {
                return isOneThread;
            }
            set
            {
                isOneThread = value;
            }
        }

        /// <summary>        
        /// 向工作队列添加对象，        
        /// 对象添加以后，如果已经绑定工作的事件        
        /// 会触发事件处理程序，对item对象进行处理        
        /// </summary>        
        /// <param name="item">添加到队列的对象</param>        
        public void Enqueue(T item)
        {
            lock (lockObj)
            {
                queue.Enqueue(item);
            }

            lock (lockIsWorking)
            {
                if (!isWorking)
                {
                    isWorking = true;
                    ThreadPool.QueueUserWorkItem(doUserWork);
                }
            }
        }

        /// <summary>       
        /// 处理队列中对象     
        /// </summary>       
        /// <param name="o"></param>        
        private void doUserWork(object o)
        {
            try
            {
                T item;
                while (true)
                {
                    lock (lockObj)
                    {
                        if (queue.Count > 0)
                        {
                            item = queue.Dequeue();
                        }
                        else
                        {
                            return;
                        }
                    }
                    if (!item.Equals(default(T)))
                    {
                        if (isOneThread)
                        {
                            if (UserWork != null)
                            {
                                UserWork(this, new EnqueueEventArgs(item));
                            }
                        }
                        else
                        {
                            ThreadPool.QueueUserWorkItem(obj =>
                            {
                                if (UserWork != null)
                                {
                                    UserWork(this, new EnqueueEventArgs(obj));
                                }
                            }, item);
                        }
                    }
                }
            }

            finally
            {
                lock (lockIsWorking)
                {
                    isWorking = false;
                }
            }
        }


        /// <summary>
        /// 队列事件类，继承EventArgs
        /// UserWork事件的参数，包含item对象       
        /// </summary>        
        public class EnqueueEventArgs : EventArgs
        {
            public T Item { get; private set; }


            public EnqueueEventArgs(object item)
            {
                try
                {
                    Item = (T)item;
                }
                catch (Exception)
                {
                    throw new InvalidCastException("object to T failed.");
                }
            }
        }
    }
}
